The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by plastic wall panels that is hot welded to a plastic-walled reaction plate.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions made of various fabrics that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2, 2013, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or trim panel that faces a vehicle occupant attached to a bladder member along a sealed periphery. One or both of the walls is deformable in order to provide an expandable, inflatable bladder. For example, the bladder member may have a pleated baffle (i.e., accordion-like) region that straightens out during inflation. The walls may be initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The front and back walls of a typical bladder for an active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but can also be blow molded. When formed separately, the front and back walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation that could result from the high inflation pressures during inflation and that result when a passenger impacts the bolster. The peripheral seal is formed by hot welding, for example. Hot welding involves heating of the matching surfaces and then compressing them together. Examples include hot plate welding, IR welding, and laser welding.
The bladder member is typically mounted to a reaction plate that acts as a fixed deployment base, so that the trim panel moves outward toward a passenger when the bladder member expands. The reaction plate may also be comprised of a molded thermoplastic, and a joint between the reaction plate and bladder member may typically be created by hot welding. One common type of active bolster is a passenger knee bolster built into a glove box door. In this case, the reaction plate also forms an inner wall of the door (e.g., incorporating a door latch and other features).
Conforming (i.e., complementary) surfaces on the bladder member and reaction plate have been provided for being hot-welded together. The surfaces are usually flat (i.e., planar) but may also include upstanding ribs that can penetrate into the matching surface. Imperfections in the flat surfaces (e.g., pits or other deformities) may be present because of material defects or issues related to the injection molding process (e.g., die wear). The presence of deformities can a pocket for trapping gas (i.e., atmospheric air) within the hot weld. The trapped bubbles create weak points in the welded joint which can lower the strength of the weld.